329 - The AC-Sun, a new concept for air conditioning

Transcription

1 329 - The AC-Sun, a new concept for air conditioning Søren Minds 1* and Klaus Ellehauge 2 1 AC-Sun, Rudolfgaardsvej 19, DK-8260 Viby J, Denmark 2 Ellehauge & Kildemoes, Vestergade 48 H, 2s.tv., DK-8000 Aarhus C, Denmark * Corresponding Author, smi@ac-sun.com Abstract This AC-Sun is in the process of developing a solar powered AC unit which only consumes 10% of the electricity of a conventional AC unit. The devise consists of a traditional thermal solar panel that heats water to temperatures between C. An expander, based on a Rankineprocess, uses the energy from the solar panels to operate a compressor, which through a Carnotprocess cools air in traditional air coolers. The process uses water as cooling agents both in the expander and the compressor and therefore is environment friendly. The core of the research and development project is the patented process, which consists of leading the energy from the compressor outlet back to the steam temperature on the inlet duct of the expander. The internal heat recovery ideally improves the system efficiency for cooling purposes compared to other similar systems. The developing process comprises design and production of process equipment and processing forms for paddle vanes and turbine casing as well as internal heat exchangers. A world-wide patent for the principles behind the solution has been approved through a PCT testing. The proto type test is ongoing in August / September Keywords: AC-Sun, Solar Air Conditioning, Rankine process, expander, turbo compressor 1. History The project AC-Sun started at year 2005 with the mission to develop and commercialize a thermal air conditioning solution driven by solar panels. The novelty of the product is great due to considerable power savings (a factor 10), free-of-pollution, silent cooling and better comfort. The technical content consists of research and development of a turbo expander/ compressor which is working with water as a process agent under low pressure and temperatures, and where the heat production from low temperature thermal solar panels is transformed into a low temperature compressor, which is used for cooling of air in an air conditioning device. The success criterion is to exploit a series of thermal processes, which by them selves are well-known, but never previously have been combined to one functioning unit. The world-wide patent on the principles behind the solution is entering the national phase and the company has taken the process to a stage where proof-of-concept has been achieved. 1

2 2. Technical description Condensor; 22 kw Sun collector 11 kw heat at 90 C Support- /Waste heat Ex. 12 kw heat at 85 C AC-Sun COP = 0.9 Evaporator; 10 kw Power: 0.4 kw Figure 1: Sketch showing AC-Sun used on an A/C-plant The AC-Sun devise consists of a traditional thermal solar panel using water with temperatures between C. An expander, based on a Rankine-process, uses the energy from solar panels to operate a compressor, which through a Carnot-process cools air in traditional air coolers: The system only uses water as the cooling medium and there is therefore no source of pollution. The principle is to make vacuum in a small tank and thereby lowering the temperature on the water used to cool the evaporator. A normal thermal solar collector makes hot water at a temperature from 75 to 95 C. This temperature range is very low but can be used as direct energy to the A/C-system in AC-Sun. The cooling system works all together without any use of electrical energy. The only electrical parts of the system are the ventilators and two small water pumps. Totally electrical energy used in AC-Sun is only 10% on normal A/C consumption. 2

3 T [C] Expansion ,2 Ideal Rankine / Carnot cycle with reheating Evaporation 4 3 The process uses water as cooling agents both in the expander and the compressor and therefore is environment friendly. The challenge comes from the use of water as a process agent. This means that the expander must be overheated minimum between C, as well as processing must be in two steps Condensing 9 6 Evaporation Compression 7 8 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10,0 11,0 12,0 s [kj/kg-k] Figure 2: Ideal Rankine / Carnot cycle with reheating The water steam from the vacuum tank is compressed in a small compressor like a turbo compressor on a car. The power to the turbo compressor comes from an expander connected to the solar collector. The expander and compressor works on the same spindle shaft. Energy from the solar collector makes the rotation on the expander which drives the compressor. The hurdle is the temperature in the expander the steam making the expander to rotate has to be overheated so the steam doesn t condense at the end of the expander blade. If this occurs at working speed, the lifetime for the turbine blade will be told in hours/days because of possible cavitations on the surface of the blade and later devastating the structure in the material. The temperature-help comes from the compressor. The steam produced in the evaporator gets compressed and the temperature rises to at least 230ºC in the compressor outlet. Through a small heat exchanger the energy from the compressor outlet goes to the expander inlet making the expansion possible without cavitations. The cooling and heating process is illustrated in a log PH-diagram showing the expansion and compression. 3

4 Figure 3: Log PH - diagram on AC-Sun In principle this will cause AC-Sun turning 1.0 kw heat from 0.8 to 1.0 kw cooling. Other processes have an energy efficiency value less than half this size. And the production prices for those plants are in contrast to AC-Sun significantly higher than the A/C market price. The energy transformation in the AC-Sun is 1.5 kw at 10 kw cooling capacity and can with higher inlet temperature make electrical energy in a generator. In addition it s possible to draw sterile water from the system it has only to be supplied with the same amount of untreated water. Maximum capacity on AC-Sun occurs after noon when the sun heats the most and the plant is controlled by a simple electrical system with low energy consumption. The pipeline layout including certain KEY-numbers is seen in figure 4. The system has been modelled in EES [1] with the adequate thermodynamic equations giving the performance of the system under specific conditions. 4

5 Furthermore the EES is in the process of being integrated in a TRNSYS [2] model, which will be used to estimate the yearly performance of the systems under different climates, as well as to optimise the dimensions etc. of the overall system. Cooling Capacity 9,904 [kw] COP = 0,8765 [kw/kw] Outdoor temp. 1 AC-Sun Solar Powered AC plant 28 [C] RH outdoor = 0,3 [RH] 11,3 [kw] 90,03 [C] 2,506 [m 3 /h] Tout 16 = 218,1 [C] 16 16,42 [kg/h] Expander 17 Expander 13 2 [kw/k] Compressor 18 Compressor 14,15 [C] [m 3 /h] 16,3 [C] 14,8 [kg/h] Tc cond = 35,27 [C] 23,3 [C] TL opv = 7 [C] RH in,max = 0,6 8 Air supply 3200 [m 3 /h] 37,76 [C] [m 3 /h] 2 [kw/k] 7 9,087 [kw] 28 [C] 2 [kw/k] 9,958 [kw] Water supply 0 [kg/h] 32,66 [C] 0,3 [RH] Air sup = 500 [m 3 /h] GF = 200 [m 2 ] Q sup = -0,7511 [kw] W evap = 0 [kg/h] dp sup = 15,1 [C] dp ude = 8,827 [C] Q evap = 0 [kw] 3. Manufacture Figure 4: The pipeline layout including certain KEY-numbers The AC-Sun is planned to be produced in unit sizes with a 10 kw cooling capacity each. Each unit can be mounted together to make a larger cooling capacity, multiplying numbers of AC- Sun units to satisfy the needs for air condition. Operating Conditions T Outside from 25 C to 45 C at 100% humidity Air Inlet Conditions T Inlet from 16 C to 24 C Maintaining fixed temperature Cooling Capacity 10 kw each unit Power Consumption Fans and pumps = 0.4 kw 10% on normal A/C consumption of electricity Materials Turbine: aluminum, cast aluminum, stainless steel 5

6 All other materials has a format like traditional air condition plants Solar collector 12 kw capacity at T Sun from 75 C to 95 C FIGURE 5: A/C-UNIT USING AC-SUN - DIM 1,2X0.8X0.6 [m] WITHOUT SOLAR COLLECTOR COOLING CAPACITY / COEFFICIENT OF PERFORMANCE Cooling capacity: CC in [kw] Cooling Of Performance: Coefficient Of Performance 90% 70% Air humidity (RH%) on 50% Supply Air to condenser 30% CC [kw] Temp. Outside [ C] Air humidity (RH%) on Supply Air to condenser 90% 70% 50% 30% COP Temp. Outside [ C] 30 FIGURE 5: COOLING CAPACITY FIGURE 6: COP 6

7 The cooling capacity, fig. 5, depends partly on the condenser efficiency. This efficiency can be changed by spaying water in the air to the condenser and thereby raise the air humidity in the supply air. 4. Status of the project The developing process has comprised design and production of process equipment and processing forms for paddle vanes and turbine casing as well as internal heat exchangers. Although there are substantial technological challenges to be solved related to the design, construction and test of the proto type, the primary challenge is to end up with a system that is commercially competitive. Design and construction of prototype The design of the turbines together with the bearing systems was fulfilled at the end of February. The conceptual design gave adequate data to produce the 4 different turbine parts and further design of the turbine house, the bearing system, the spindle etc. all to manage high speed on the spindles. The turbine parts were delivered in the start of April and installed together with the external components (evaporator, condensers, fans etc.). The turbine sealings/washers were later changed to manage adequate higher temperatures. Through the sampling of the parts several changes were made e.g on the sealing on the connections between external parts for keeping a specific vacuum in the pipelines. Testing The external cooling and heating components have been designed, produced and mounted/installed for test purpose e.g. prepared for vacuum, setting up for optimal measurement of temperature, pressure etc. Furthermore a PC and a data logger has been installed to make the measurement on different temperatures and pressures around the turbines and external components. The RPM-counter uses light to measure the speed - the power used to heat the water (in stead of a solar collector) is measured; PCprograms to calculate the performance on the proto type using test data (temp., pressure, RPM, power) are completed. 7

8 Test series on the proto type are going on in august Report on the test results will firstly be available on Newest: Logged data from the first tests on the proto type gives positive results and confirms the function in the design. The expander delivers the compressor capacity as expected and used in the cooling process for air condition. Plans for further testing The proto type test is followed up by making 3-5 test units mounted with solar panels and placed around in the surroundings mainly in the southern Europe for optimal test conditions. 5. Conclusion The AC-Sun system is a new concept for solar driven air-condition. It is expected to have much higher efficiency than other soar driven systems as well as it is expected to be manufactured to much lower cost than other solar driven systems. If expectations are met the system should have the potential to overcome market barriers for solar driven air-condition. The challenge has been the design and construction of the steam driven turbine which rotate at very high speed. For the moment (August 2008) a prototype had been constructed and is being tested. The testing until now has detected problems which have been solved. If the further testing in the coming months perform successful further prototypes will be produced and tested under real conditions in Southern Europe. The AC-Sun system is reported and modelled as part of the Danish participation in IEA SHC Task 38 Solar Airconditioning and Refrigeration References [1] S.A.Klein, ( ). EES (Engineering Equation Solver) PC-program, F-Chart Software [2] TRNSYS (TRaNsient SYstems Simulation program), 2002 The Board of Regents of the University of Wisconsin System. 8